1. Field of the Invention
The present invention relates to an electronic control system which is capable of detecting a computer malfunction by monitoring operations of a plurality of computers with respect to each other.
2. Related Art
Electronically-controlled throttle devices, which drive throttle valves by electric motors, are used recently in automotive vehicles. JP-A-6-83659 discloses a method of detecting malfunction of microcomputer (computer) for such electronically-controlled throttle devices. According to this malfunction detection method, a plurality of computers communicate and compare each other's various calculation data and A/D conversion data, which are produced in each computer in the same calculation and A/D conversion processing, so that the computer malfunction may be detected based on the comparison of data.
It is, however, impossible to determine which one of the computers are in failure when two computers is used in the system. Therefore, both computers will have to be disabled for a fail-safe operation upon detection of the malfunction.
For instance, recent electronic control systems for engines use a computer for a throttle control as well as a computer for an engine control (spark ignition and fuel injection control). In those systems, even if only the computer for the throttle control fails, both computers have to be disabled to control the spark ignition and fuel injection. As a result, a limp-home operation is not sufficiently ensured.
To overcome the above disadvantage, an additional computer for monitoring other computers may be used, or a watch dog timer (WDT) may be added to the engine control computer. The additional computer will add cost. Further, the engine control computer will not be able to detect the malfunction of a monitor program of the throttle control computer by only the watch dog timer of the engine control computer in the event that only the monitor program of the throttle control computer fails.